Skin cancer is the most common form of cancer, accounting for one-third of all cancer diagnoses in the United States. This translates to 1 out of 5 Americans developing skin cancer at some point in their lifetime. There are three different primary types of skin cancer based on the type of skin cells that are affected: basal cell carcinoma, squamous cell carcinoma, and melanoma. The non-melanoma cancer types are more frequent, but highly curable. Melanoma, while less common, is much more deadly, causing over 75% of skin cancer deaths. There were an estimated 81,000 new cases and 12,000 deaths resulting from melanoma in 2012. More than 3 million non-melanoma skin cancers and 140,000 melanoma skin cancers afflict people every year in the United States; this translates to one out of every three cancers. Skin cancer incidence and mortality rates are increasing significantly, faster than any other type of cancer. These rates have been steadily rising for both men and women for at least the past 30 years and of the seven most common cancers in the US, melanoma is the only one whose incidence is increasing. Both incidence and mortality rates have a strong positive association with age, are higher for non-Hispanic white males, and most often occur on the trunk and upper extremities. Genetic risk factors and excessive sun exposure are the most common causes of skin cancer.
Increases in incidence have been attributed to expanded skin screenings and the increased detection of tumors with low metastatic potential. Many consider the increased diagnosis rate to arise from evaluation of thinner tumors, but there is also a continued increase in the diagnosis of more fatal, thick (>4 mm) tumors.
A human's skin is made up of three distinct layers: the epidermis, dermis, and hypodermis. Each layer is composed of different types of skin cells. The epidermis, or outermost layer of skin, is made up of squamous cells. Basal cells line the dermal-epidermal junction that separates the two layers. Melanocytes, or melanin producing cells, are spread sporadically within these basal cells. Melanin acts as a filter by using its darker color to absorb UV light. This can protect the hypodermis—which is primarily fatty tissue and vasculature—as well as other internal tissue from dangerous radiation. Cancer can develop when DNA within the skin cells becomes damaged and the body is unable to repair the damage. These damaged cells begin to grow and divide. As the damaged cells multiply, they form a tumor. Since skin cancer generally develops in the epidermis, or outermost layers of skin, a tumor is usually clearly visible. This makes most skin cancers detectable in the early stages.
Identifying skin cancer in its early stages is extremely important to ensure a better chance of survival. Melanoma initially grows horizontally within the epidermis and then after time starts to penetrate into the dermis. Tumor thickness is statistically the most powerful indicator of survival. Probability of survival is inversely related to tumor thickness. Survival rate is greatest for a localized melanoma. Three out of every four melanomas are diagnosed at this stage. If the tumor is less than 0.76 mm, there is a 99% chance for ten-year survival; however this survival percentage drops to less than 50% for a tumor thickness greater than 3 mm. This is due to the increasing potential of melanoma to metastasize as it grows into the dermis making it extremely critical to detect skin cancer in its early stages.
The gold standard for diagnosis has been invasive biopsy and excision, followed by histological and pathological examination. Studies have found that the ratio of biopsies of benign lesions to malignant ones can be as high as 500 to one, while at the same time, one-third of skin cancers are missed. Such statistics show that our current practices have neither specificity nor sensitivity, and a better solution is required.
When a lesion is determined to be cancerous via biopsy, the physician determines the boundaries for excision using a completely subjective visual observation; the only way to verify that the entire lesion was excised is by performing a time-consuming pathology test on the tissue after it has been excised. This method can result in repeat procedures to remove a single lesion, which is inefficient, risks infection, and is cosmetically unappealing.
The effectiveness of the primary treatment method, surgical excision, hasn't changed for decades, but the survival rate has improved—primarily due to earlier detection. It is clear that the single most promising strategy to reduce the mortality rate from melanoma is early detection. Earlier detection also decreases cost. Late stage melanoma is approximately 32 times more expensive than early stage tumors. High costs warrant an increased emphasis on developing effective strategies for early diagnosis.
The key to improving survival rates is early detection. Five-year survival rates for melanoma drop from 98% to 16% and average costs rise as the disease progresses from an early to a late stage. A patient's first point of contact, their primary physician, has significantly lower accuracy when diagnosing skin lesions than dermatologists. With increasing wait times for dermatologists, there is a huge gap in the market for cost-effective detection tool for non-specialists. The healthcare system would save over $260 million per year by reducing unnecessary biopsies and helping patients catch cancer earlier.
Even though early diagnosis almost guarantees survival, the U.S. Preventive Services Task Force concluded there wasn't enough evidence to support routine screening by primary care physicians. This is partially due to the fact there is a considerable debate on who should be screened, who should do the screening, and how often the screening should occur. There are also millions of high-risk melanoma patients with several abnormally appearing lesions. It is impossible to predict which lesions will become cancerous and the excision of all is not practical, requires unnecessary surgery, and does not completely prevent the chance of skin cancer.
Even without routine screening, the majority of patients detect their own melanoma. However, studies have shown that physicians detect melanoma sooner, while it is thinner in its earlier stages. Experience is critical when it comes to detecting early stage melanoma using current methods. The ability to accurately detect melanoma varies widely between individual dermatologists and accuracy drops significantly for non-dermatologists.